It's important to put what you learn into practice.
Using design to solve a real problem allows you to demonstrate that you know what you're doing. It shows that you know how to take the output of skill X and use it as the input into skill Y.
If you're new to UX design and want to get a job as a designer, or are already a UX designer and want a new job, it's important to have a portfolio that shows off your skills. Your portfolio portfolio should feature case studies that explain how you found a problem, understood it, and solved it with design.
In that way, practice projects don't just help you to remember what you've learned. They also help you to get a job.
Practice projects give you a chance to show off every UX skill you have. The only limit is how much time you're willing to put in.
To start a practice project, all you need is a real problem. By "real" I mean a problem that people actually have, and not one that you've made up. If you're solving your own made up problem, there's no easy way to make sure that your design works.
Businesses are full of problems that need to be solved. If you've already got a job, even if you don't work as a UX designer, you might find that the people around you have problems that you could design a solution for. Maybe your co-worker uses a piece of software to do their work, but it's not very good. How would you improve it?
Your friends and family might have all sorts of problems that design could help to solve. "I went to the supermarket and forgot half of what I needed to buy by the time I got there." How could you use design to help this person remember what they need ?
Nothing is perfectly designed. Every app or website you come across will have problems that design could solve. How could you find out what those problems are, and how would you solve them?
There are many design briefs on the internet: Pre-written design problems that you can pick up and start work on immediately. Type "UX design briefs" into your favourite search engine.
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